Myngo is a jQuery frontend written in Python using Tornado. It’s relatively attractive and reminds me a lot of Futon. If Python is your thing, check this out.
Mongo3 is a beautiful interface focused on managing clusters, written in Ruby using the Sinatra framework. It’s an easy gem install if you have Ruby ready to go.
futon4mongo is a port of the popular CouchDB utility Futon. Its goal seems to be to match it feature for feature. It is written in Ruby using Sinatra, and was the first web UI I explored for MongoDB. It’s reasonably stable and works for a basic view into your data quite nicely.
phpMoAdmin is a themeable PHP administration tool in a single 90kb file (hrm) with zero configuration. Ok, I have to admit, the prospect of looking at or even trying to contribute to the code for this project REALLY scares me, but you have to admire the ease of dropping a single PHP file in and starting to use the web to administer MongoDB. Give it a shot if PHP is your thing.
Opricot is an Apache+PHP tool for administering MongoDB. It looks a little easier to use and more feature-filled than phpMoAdmin at this time.
I don’t know much about this product, but MongoHub is a native OS X GUI for MongoDB. It’s very fresh so it isn’t very feature-filled yet, but you can create multiple connections, browse collections, and run queries. It looks to be the start of a potentially very cool tool for OS X.
Do you know of any other UI tools for MongoDB I may have missed? If so, let me know in the comments!